This invention relates to telecommunications switching systems and in particular to time division switching systems.
Time division telecommunications switching systems commonly utilize port circuits (such as line and trunk circuits) which contain a recirculating ring counter driven by the system clock. In order to connect the port circuit to a common bus to permit communications interchange, a one-bit is written into a stage of the ring counter. The one-bit circulates through the ring counter under control of the system clock and upon reaching a predetermined location, it enables time division switches which connect the port circuit to the common bus. If the ring counter is provided with one stage for each time slot in the system, the one-bit will appear at the predetermined location each time the system cycles through all of the time slots. The port circuit is designated as being assigned the time slot which corresponds to the ring counter stage in which the one-bit is written.
Since there is a one-to-one correspondence between the number of time slots and the number of stages in the port circuit ring counters, the prior art has required different port circuits for different numbers of time slots. Accordingly, a problem in the prior art has been that expensive and coupled physical equipment changes have been required for increasing or decreasing line and trunk ports in a switching system. Such changes frequently are demanded by customers to fulfill dynamic service needs. Unfortunately, they tend to increase outage time of the system and contribute to higher cost service and inventory.
It is apparent that there is a need for a system which can operate with various numbers of time slots while utilizing the same port circuit and ring counter circuitry.
Accordingly, it is an object of the present invention to allow various size switching systems to utilize the same port circuit.
It is a further object of the present invention to minimize the number of modifications necessary to change the size of a switching system.